1. Field of the Invention
The present invention relates to an exposure method, and in particular, to an exposure method for increasing uniformity of a critical dimension on a shot-to-shot level on the same wafer in a wafer acceptable test (WAT) step.
2. Description of Related Art
In a manufacturing process of an integrated circuit, a photolithography process is used to transfer customized circuit patterns on a photo mask to thin films formed on a wafer. An image transferring process includes forming a photoresist layer on a non-process layer. Then, the photoresist layer is illuminated through a photo mask having the customized circuit patterns. After that, a developing process is performed on the photoresist layer. Thereafter, an etching process is performed on the non-process layer by using a patterned photoresist layer as a mask. Hence, the image transferring process is accomplished.
Generally, one of basic parameters affecting a critical dimension (CD) in the photolithography process is mainly an exposure dose. Traditionally, CD control in the photolithography process includes compensating the exposure dose according to the measured CD after an exposure process is performed and providing a predetermined exposure dose by an energy set-up system, so that the CD of the wafers in a next lot can be closer to a target value. The exposure dose can be measured by measuring a photoresist pattern on the wafer manufactured by the apparatus, and an automatic feedback process is performed on the exposure apparatus according to/based on a result of measurement. The exposure apparatus is operated under good control of the parameters by using an advanced process control (APC), for example.
Product variations among the same products manufactured through different tool paths can be eliminated by using an automatic feedback system of the APC when the same products are manufactured massively through a plurality of the tool paths formed by arranging a plurality of manufacturing apparatuses, thereby increasing uniformity of product quality on a wafer-to-wafer level. Because of apparatus designs and wafer positions, pattern transformation among every exposure region on the same wafer has some little variations in a yellow light manufacturing process. As a device is increasingly miniaturized, variations of the CDs among different exposure regions on the same wafer affect an electrical property of a subsequently manufactured product significantly. However, the conventional automatic feedback system only provides a fixed feedback value for every wafer in every lot, which is not helpful in controlling the variations of the CDs among every exposure region on the wafer.